1. Field of the Invention
The present invention relates to a paper feeding cassette for use in an image forming apparatus such as a facsimile apparatus, which has a structure allowing the user to change the size of sheets to be accommodated therein as desired by the user.
2. Description of the Related Art
Conventionally, a paper feeding cassette for use in an image forming apparatus such as a facsimile apparatus has a structure capable of accommodating sheets of various sizes as desired by the user. Further, such a paper feeding cassette is so structured as to be capable of restricting the width and the feeding orientation of sheets to be accommodated in accordance with the size of the sheets for preventing the occurrence of paper jam or the like due to feeding of such a sheet in a skewed fashion.
A prior art paper cassette capable of restricting the feeding orientation of sheets accommodated in the cassette is disclosed in Japan Patent Laid Open Publication Hei No. 7-309458. In the paper cassette disclosed in this patent publication, a bottom plate bearing the leading edge side of a stack of sheets thereon is pressed upward by a spring to bring the sheets into contact with a sheet feeding roller, while a rear plate attached to the paper feeding cassette restricts the position of the trailing edge of the stack of sheets. On the other hand, Japan Patent Laid Open Publication Hei No. 10-77123 discloses a paper cassette in which a push-up plate bearing a stack of sheets entirely thereon is pressed upward by a spring to bring the sheet stack into contact with a sheet feeding roller, while a trailing edge guide removably attached to the push-up plate restricts the position of the trailing edge of the sheet stack.
In the structure of the paper feeding cassette disclosed in Japan Patent Laid Open Publication Hei No. 7-309458, the bottom plate needs to be located so as not to interfere with the rear plate. Therefore, the space allowing the rear plate to be disposed therein is limited, and the rear plate needs to be located closer to the front side of the cassette as the size of sheets used becomes smaller. Therefore, the bottom plate located so as not to interfere with the rear plate has to be inclined at a relatively large angle (inclination), which causes the sheets stacked thereon to be warped. When the sheets are warped, their frictional resistance increases, which may cause a failure of the sheet feeding roller in catching a sheet before feeding. Further, if sheets are accommodated in the paper feeding cassette for a long period, such sheets become kept in a warped state, which may cause paper jam in transferring the sheets.
On the other hand, the paper feeding cassette disclosed in Japan Patent Laid Open Publication Hei No. 10-77123 is so structured to receive a stack of sheets entirely on the push-up plate provided with the trailing edge guide thereon. Therefore, unlike the paper feeding cassette disclosed in Japan Patent Laid Open Publication Hei No. 7-309458, warping of sheets will not occur, which prevents the catching failure of the sheet feeding roller as well as paper jam in transferring the sheets.
However, since the trailing edge guide is mounted as inserted in the push-up plate, the cassette can hold only sheets of predetermined sizes and hence cannot accommodate sheets of nonstandard sizes. Further, the trailing edge guide is detachable from the push-up plate and can be stored in the paper feeding cassette when unnecessary, which may cause the trailing edge guide to be lost.